1 7z Format description (2.30 Beta 25) 2 ----------------------------------- 3 4 This file contains description of 7z archive format. 5 7z archive can contain files compressed with any method. 6 See "Methods.txt" for description for defined compressing methods. 7 8 9 Format structure Overview 10 ------------------------- 11 12 Some fields can be optional. 13 14 Archive structure 15 ~~~~~~~~~~~~~~~~~ 16 SignatureHeader 17 [PackedStreams] 18 [PackedStreamsForHeaders] 19 [ 20 Header 21 or 22 { 23 Packed Header 24 HeaderInfo 25 } 26 ] 27 28 29 30 Header structure 31 ~~~~~~~~~~~~~~~~ 32 { 33 ArchiveProperties 34 AdditionalStreams 35 { 36 PackInfo 37 { 38 PackPos 39 NumPackStreams 40 Sizes[NumPackStreams] 41 CRCs[NumPackStreams] 42 } 43 CodersInfo 44 { 45 NumFolders 46 Folders[NumFolders] 47 { 48 NumCoders 49 CodersInfo[NumCoders] 50 { 51 ID 52 NumInStreams; 53 NumOutStreams; 54 PropertiesSize 55 Properties[PropertiesSize] 56 } 57 NumBindPairs 58 BindPairsInfo[NumBindPairs] 59 { 60 InIndex; 61 OutIndex; 62 } 63 PackedIndices 64 } 65 UnPackSize[Folders][Folders.NumOutstreams] 66 CRCs[NumFolders] 67 } 68 SubStreamsInfo 69 { 70 NumUnPackStreamsInFolders[NumFolders]; 71 UnPackSizes[] 72 CRCs[] 73 } 74 } 75 MainStreamsInfo 76 { 77 (Same as in AdditionalStreams) 78 } 79 FilesInfo 80 { 81 NumFiles 82 Properties[] 83 { 84 ID 85 Size 86 Data 87 } 88 } 89 } 90 91 HeaderInfo structure 92 ~~~~~~~~~~~~~~~~~~~~ 93 { 94 (Same as in AdditionalStreams) 95 } 96 97 98 99 Notes about Notation and encoding 100 --------------------------------- 101 102 7z uses little endian encoding. 103 104 7z archive format has optional headers that are marked as 105 [] 106 Header 107 [] 108 109 REAL_UINT64 means real UINT64. 110 111 UINT64 means real UINT64 encoded with the following scheme: 112 113 Size of encoding sequence depends from first byte: 114 First_Byte Extra_Bytes Value 115 (binary) 116 0xxxxxxx : ( xxxxxxx ) 117 10xxxxxx BYTE y[1] : ( xxxxxx << (8 * 1)) + y 118 110xxxxx BYTE y[2] : ( xxxxx << (8 * 2)) + y 119 ... 120 1111110x BYTE y[6] : ( x << (8 * 6)) + y 121 11111110 BYTE y[7] : y 122 11111111 BYTE y[8] : y 123 124 125 126 Property IDs 127 ------------ 128 129 0x00 = kEnd, 130 131 0x01 = kHeader, 132 133 0x02 = kArchiveProperties, 134 135 0x03 = kAdditionalStreamsInfo, 136 0x04 = kMainStreamsInfo, 137 0x05 = kFilesInfo, 138 139 0x06 = kPackInfo, 140 0x07 = kUnPackInfo, 141 0x08 = kSubStreamsInfo, 142 143 0x09 = kSize, 144 0x0A = kCRC, 145 146 0x0B = kFolder, 147 148 0x0C = kCodersUnPackSize, 149 0x0D = kNumUnPackStream, 150 151 0x0E = kEmptyStream, 152 0x0F = kEmptyFile, 153 0x10 = kAnti, 154 155 0x11 = kName, 156 0x12 = kCreationTime, 157 0x13 = kLastAccessTime, 158 0x14 = kLastWriteTime, 159 0x15 = kWinAttributes, 160 0x16 = kComment, 161 162 0x17 = kEncodedHeader, 163 164 165 7z format headers 166 ----------------- 167 168 SignatureHeader 169 ~~~~~~~~~~~~~~~ 170 BYTE kSignature[6] = {'7', 'z', 0xBC, 0xAF, 0x27, 0x1C}; 171 172 ArchiveVersion 173 { 174 BYTE Major; // now = 0 175 BYTE Minor; // now = 2 176 }; 177 178 UINT32 StartHeaderCRC; 179 180 StartHeader 181 { 182 REAL_UINT64 NextHeaderOffset 183 REAL_UINT64 NextHeaderSize 184 UINT32 NextHeaderCRC 185 } 186 187 188 ........................... 189 190 191 ArchiveProperties 192 ~~~~~~~~~~~~~~~~~ 193 BYTE NID::kArchiveProperties (0x02) 194 for (;;) 195 { 196 BYTE PropertyType; 197 if (aType == 0) 198 break; 199 UINT64 PropertySize; 200 BYTE PropertyData[PropertySize]; 201 } 202 203 204 Digests (NumStreams) 205 ~~~~~~~~~~~~~~~~~~~~~ 206 BYTE AllAreDefined 207 if (AllAreDefined == 0) 208 { 209 for(NumStreams) 210 BIT Defined 211 } 212 UINT32 CRCs[NumDefined] 213 214 215 PackInfo 216 ~~~~~~~~~~~~ 217 BYTE NID::kPackInfo (0x06) 218 UINT64 PackPos 219 UINT64 NumPackStreams 220 221 [] 222 BYTE NID::kSize (0x09) 223 UINT64 PackSizes[NumPackStreams] 224 [] 225 226 [] 227 BYTE NID::kCRC (0x0A) 228 PackStreamDigests[NumPackStreams] 229 [] 230 231 BYTE NID::kEnd 232 233 234 Folder 235 ~~~~~~ 236 UINT64 NumCoders; 237 for (NumCoders) 238 { 239 BYTE 240 { 241 0:3 DecompressionMethod.IDSize 242 4: 243 0 - IsSimple 244 1 - Is not simple 245 5: 246 0 - No Attributes 247 1 - There Are Attributes 248 7: 249 0 - Last Method in Alternative_Method_List 250 1 - There are more alternative methods 251 } 252 BYTE DecompressionMethod.ID[DecompressionMethod.IDSize] 253 if (!IsSimple) 254 { 255 UINT64 NumInStreams; 256 UINT64 NumOutStreams; 257 } 258 if (DecompressionMethod[0] != 0) 259 { 260 UINT64 PropertiesSize 261 BYTE Properties[PropertiesSize] 262 } 263 } 264 265 NumBindPairs = NumOutStreamsTotal - 1; 266 267 for (NumBindPairs) 268 { 269 UINT64 InIndex; 270 UINT64 OutIndex; 271 } 272 273 NumPackedStreams = NumInStreamsTotal - NumBindPairs; 274 if (NumPackedStreams > 1) 275 for(NumPackedStreams) 276 { 277 UINT64 Index; 278 }; 279 280 281 282 283 Coders Info 284 ~~~~~~~~~~~ 285 286 BYTE NID::kUnPackInfo (0x07) 287 288 289 BYTE NID::kFolder (0x0B) 290 UINT64 NumFolders 291 BYTE External 292 switch(External) 293 { 294 case 0: 295 Folders[NumFolders] 296 case 1: 297 UINT64 DataStreamIndex 298 } 299 300 301 BYTE ID::kCodersUnPackSize (0x0C) 302 for(Folders) 303 for(Folder.NumOutStreams) 304 UINT64 UnPackSize; 305 306 307 [] 308 BYTE NID::kCRC (0x0A) 309 UnPackDigests[NumFolders] 310 [] 311 312 313 314 BYTE NID::kEnd 315 316 317 318 SubStreams Info 319 ~~~~~~~~~~~~~~ 320 BYTE NID::kSubStreamsInfo; (0x08) 321 322 [] 323 BYTE NID::kNumUnPackStream; (0x0D) 324 UINT64 NumUnPackStreamsInFolders[NumFolders]; 325 [] 326 327 328 [] 329 BYTE NID::kSize (0x09) 330 UINT64 UnPackSizes[] 331 [] 332 333 334 [] 335 BYTE NID::kCRC (0x0A) 336 Digests[Number of streams with unknown CRC] 337 [] 338 339 340 BYTE NID::kEnd 341 342 343 Streams Info 344 ~~~~~~~~~~~~ 345 346 [] 347 PackInfo 348 [] 349 350 351 [] 352 CodersInfo 353 [] 354 355 356 [] 357 SubStreamsInfo 358 [] 359 360 BYTE NID::kEnd 361 362 363 FilesInfo 364 ~~~~~~~~~ 365 BYTE NID::kFilesInfo; (0x05) 366 UINT64 NumFiles 367 368 for (;;) 369 { 370 BYTE PropertyType; 371 if (aType == 0) 372 break; 373 374 UINT64 Size; 375 376 switch(PropertyType) 377 { 378 kEmptyStream: (0x0E) 379 for(NumFiles) 380 BIT IsEmptyStream 381 382 kEmptyFile: (0x0F) 383 for(EmptyStreams) 384 BIT IsEmptyFile 385 386 kAnti: (0x10) 387 for(EmptyStreams) 388 BIT IsAntiFile 389 390 case kCreationTime: (0x12) 391 case kLastAccessTime: (0x13) 392 case kLastWriteTime: (0x14) 393 BYTE AllAreDefined 394 if (AllAreDefined == 0) 395 { 396 for(NumFiles) 397 BIT TimeDefined 398 } 399 BYTE External; 400 if(External != 0) 401 UINT64 DataIndex 402 [] 403 for(Definded Items) 404 UINT32 Time 405 [] 406 407 kNames: (0x11) 408 BYTE External; 409 if(External != 0) 410 UINT64 DataIndex 411 [] 412 for(Files) 413 { 414 wchar_t Names[NameSize]; 415 wchar_t 0; 416 } 417 [] 418 419 kAttributes: (0x15) 420 BYTE AllAreDefined 421 if (AllAreDefined == 0) 422 { 423 for(NumFiles) 424 BIT AttributesAreDefined 425 } 426 BYTE External; 427 if(External != 0) 428 UINT64 DataIndex 429 [] 430 for(Definded Attributes) 431 UINT32 Attributes 432 [] 433 } 434 } 435 436 437 Header 438 ~~~~~~ 439 BYTE NID::kHeader (0x01) 440 441 [] 442 ArchiveProperties 443 [] 444 445 [] 446 BYTE NID::kAdditionalStreamsInfo; (0x03) 447 StreamsInfo 448 [] 449 450 [] 451 BYTE NID::kMainStreamsInfo; (0x04) 452 StreamsInfo 453 [] 454 455 [] 456 FilesInfo 457 [] 458 459 BYTE NID::kEnd 460 461 462 HeaderInfo 463 ~~~~~~~~~~ 464 [] 465 BYTE NID::kEncodedHeader; (0x17) 466 StreamsInfo for Encoded Header 467 [] 468 469 470 --- 471 End of document 472
